Is it ever right to yell?

Recently I was in charge of a network installation project. I had a small team working for me and one of the members started distracting and “fooling” around not doing the work I had assigned to them. I raised my voice when I asked her to stop messing around and get back to work and some of the other members of the team pulled me aside afterwards. They told me I should appologize to the other member and that I had no right to “Yell” at her. I didn’t see myself as yelling just being stern with her to get her to start working, so I didn’t appologize. Am I wrong to have rose my voice with her and should I appologize for it? Is there ever an acceptable time to yell at an employee?